1. Technical Field
The present invention relates to a liquid-level detecting apparatus for detecting a level of a liquid surface and, more particularly, to detecting a level of fuel in a vehicle.
2. Brief Description of the Related Art
A related art liquid-level detector in the fuel tank or the liquid tank detects a variation of the level of a liquid surface by using a conductive sliding arm that rotates in cooperation with a float floating on the liquid surface. The conductive sliding arm slides on a detector plate, and a value of combined resistors connected to conductive segments formed at substantially equal intervals on an insulating substrate of the detector plate or a voltage value based on the combined resistance value is measured corresponding to the rotation of the conductive sliding arm.
For example, JP-A-2003-257717 describes such a related art liquid-level detector. JP-A-2003-257717 also describes a method for trimming the resistors of the liquid-level detector to adjust a resistance value to a desired resistance value.
FIG. 7 is schematic view of a related art liquid-level detector. FIG. 8 is an enlarged front view of the detector plate shown in FIG. 7.
The related art liquid-level detector 100 shown in FIG. 7 is described in JP-A-2003-257717. Here, the liquid-level detector is briefly described by referring to FIGS. 7 and 8.
As shown in FIG. 7, in the related art liquid-level detector 100, a float 101 floating on a liquid surface L in a fuel tank for accommodating fuel of a motor vehicle is connected to an end part of a connector arm 102 and a base end side of the connector arm 102 is supported by a detector main body 103 so as to freely rotate.
Further, in the detector main body 103, a conductive sliding arm 104 having an electric conductivity is provided so as to rotate about a center P of rotation in cooperation with the rotation of the connector arm 102. Further, the conductive sliding arm 104 slides on a detector plate 110 provided in the detector main body 103 in accordance with the rotation of the connector arm 102.
Then, as described by FIG. 8, the conductive sliding arm 104 that rotates through the connector arm 102 in cooperation with the float 101 floating on the liquid surface L is allowed to slide on the detector plate 110. Resistors 113 are connected respectively to first conductive segments 112 and are formed to be mounted on the conductive segments 112 on an insulating substrate 111 of the detector plate 110. A combined resistance value of the resistors 113 or a voltage value based on the combined resistance value is measured corresponding to the rotation of the conductive sliding arm 104 to detect the level of the liquid surface L.
Here, as shown in an enlarged view in FIG. 8, in the above-described detector plate 110, first conductive segments 112 are formed in a rectangular shape in an area of the upper part of the insulating substrate 111 that is separated from the center P of the rotation of the conductive sliding arm 104, and mutually adjacent conductive segments 112 are connected together through the resistors 113.
Further, in an area of the lower part of the insulating substrate 111 that is closer to the center P of the rotation of the conductive sliding arm 104, a conductive section 114 is formed. In the conductive section 114, second conductive segments 114a are formed correspondingly to the first conductive segments 112.
Further, at one end side of the first conductive segments 112, a first end part land 112a is formed. At one end side of the second conductive segments 114a, a second end part land 114b is formed. A measuring device 115 is connected between the first and second end part lands 112a and 114b. 
In the right part of FIG. 8, a state is shown that the resistance value of a suitable resistor 113 formed between the mutually adjacent first conductive segments 112 and 112 is adjusted to a desired value by a trimming T.
On the conducting sliding arm 104 having the electric conductivity, a first contact part 104a that selectively comes into sliding contact with the first conductive segments 112 and a second contact part 104b that selectively comes into sliding contact with the second conductive segments 114a are provided that are spaced away from each other.
Then, when the conductive sliding arm 104 rotates on the center P of the rotation, the first and second contact parts 104a and 104b selectively come into sliding contact with the first and second conductive segments 112 and 114a corresponding to the rotating position of the conductive sliding arm 104.
In the related art liquid-level detector 100, when the conductive sliding arm 104 rotates on the center P of the rotation through the connector arm 102 in cooperation with the float 101 floating on the liquid surface L, only the resistors 113 existing between a segment 112 with which the first contact part 104a comes into sliding contact and the first end part land 112a connected to the first conductive segment 112 disposed at the other end side are connected in series to the measuring device 115 as shown by an arrow of FIG. 8, so that a combined resistance value of the resistors 113 can be measured by the measuring device 115 to detect the level of the liquid surface L in accordance with the combined resistance value or the voltage value based on the combined resistance value.
In the related art liquid-level detector 100, the variation of the float 101 floating on the liquid surface L is transferred to the connector arm 102 and the conductive sliding arm 104, and the level of the liquid surface L can be detected in accordance with the combined resistance value of the resistors 113 existing between the segment 112 with which the first contact part 104a comes into sliding contact correspondingly to the rotating position of the conductive sliding arm 104 sliding on the resistance plate 110 and the first end part land 112a or the voltage value based on the combined resistance value. In the detector plate 110, a material of the resistors 113 or a pattern width B of the first conductive segments 112 formed on the insulating substrate 111 is preset in order that the liquid-level detector 100 may be mass-produced.
However, in the previously standardized resistance plate 110, the resistor 113 formed between the first conductive segments 112 and 112 that are adjacent to each other on the insulating substrate 111 is desired to be changed to a value smaller than a resistance value set at the time of standardization from a user.
Moreover, the geometry of the liquid-level detector 110 creates constraints in the detector plate 110. For example, a rotation range of the conductive sliding arm 104 is typically set in advance to rotate within a range of rotating angle of, for example, 70°. Further, it is typical for the combined resistance value of the resistors 113 to be about 10Ω within a range of 10° of rotation of the conductive sliding arm 104. However, there is a disadvantage in the related art liquid-level detector 100 in that when the user requests to obtain the combined resistance value or the voltage value based on the combined resistance value of about 5Ω substantially half times or less as high as the above-described value at the time of the standard design within the range of 10° due to a reason of the form of a fuel tank not shown in the drawing, since the previously standardized resistance plate 110 cannot be directly applied, an inconvenience occurs.
Additionally, since in the above cases, in order to change the material of the resistors 113, and to change the pattern width B of the segments 112, redesign of the resistance plate 110 is required, a design cost and production cost are greatly increased, and the related art liquid-level detecting unit 100 cannot be rapidly and inexpensively provided.
Thus, a liquid-level detecting apparatus is desired that a request for reducing the resistance value from a user can be simply realized to the resistors provided in the previously standardized resistance plate.